1. Field of the Invention
The present invention is directed to a scanning unit for a position-measuring apparatus, and more particularly, to a position-measuring apparatus that utilizes a flexible printed circuit to electrically couple elements which eliminates the need for bond wires.
2. Discussion of Relevant Art
In prior art optical position-measuring apparatuses, a scale having a graduation is scanned with a scanning unit for the generation of position-dependent signals. The scale graduation, in the case of a transmitted-light measuring apparatus, includes alternately disposed light-transmissive and light non-transmissive areas, for example. Furthermore, a radiation source is required that illuminates the scale graduation structure either by incident light or transmitted light. Using radiation-sensitive detector elements, shift-dependent modulated optical scanning signals are registered in the case of a relative movement of the scanning unit and scale graduation structure. In addition, customarily provided on the side of the scanning unit of a transmitted light type optical position-measuring apparatus is a scanning graduation that is also formed by a sequence of light-transmissive and light non-transmissive areas.
Traditional scanning units are relatively expensive to construct and manufacture. There have been efforts to construct components of an optical position-measuring apparatus more simply and compactly while still providing mechanical stability.
One solution is directed toward the integration of various components of the scanning unit, and, if necessary, the required evaluation electronics into a common carrier substrate. German Patent Publication DE 195 24 725 C1 discloses such an example. This proposed solution has disadvantages because expensive multi-layer systems must be produced for connecting the various components on the glass carrier substrate if conductor track crossovers are necessary.
Connecting problems of this type can be managed if flexible printed circuits are used for connecting various components within the scanning unit. These flexible printed circuits may also contain, already in more or less integrated form, various components of the scanning unit, and, if necessary, of the evaluation electronics. Scanning units with this type of flexible printed circuits are known from the following publications: European Patent Publication Nos. EP 0 328 661 A1 and EP 0 146 312; Japanese Patent Publication No. JP-57-207819 and U.S. Pat. No. 5,486,923, for example.
In each of the aforementioned publications, a flexible printed circuit is applied to a carrier component of a scanning unit and to this in turn several components such as light sources, evaluation components, or detector elements are applied. The various components are connected electrically to one another by the conductor tracks of the flexible printed circuit. The radiation-sensitive face of the detector elements is oriented oppositely to the flexible printed circuit in the variations that are known from each of these publications. This has the consequence that, in the case of connection of the detector elements from the radiation-sensitive side, so-called bond wires are required for the connection to the flexible printed circuit. This type of connection results in increased cost of manufacture, particularly for the production of a large number of parts.
In the scanning unit disclosed in Japanese Patent Publication No. JP-57-207819 the radiation-sensitive faces of the detector elements are also oriented away from the flexible printed circuit. Details regarding the connection of the detector elements are not disclosed.
U.S. Pat. No. 5,534,693 also discloses disposing on a scale graduation carrier an optoelectronic detector element by a flexible printed circuit for reference mark detection.
It is thus an object of the present invention to form advantageously a scanning unit with which a graduation structure of a scale for the generation of position-dependent output signals can be scanned. Ensured signal quality, reduced manufacturing costs should result particularly if the electrical connection points are as small as possible. Furthermore, it is desirable that the scanning unit have as compact and stable a mechanical construction as possible.
The present invention disposition of the flexible printed circuit and at least one of the detector elements within the scanning unit of an optical position-measuring apparatus has, moreover, in comparison to the prior art solutions, a clearly simpler manufacture as a consequence. Thus it is no longer required to connect electrically the detector elements to one another and/or to other structural elements by separately applied bond wires. Instead, the assembly of scanning units with the required detector elements results from the flexible printed circuit already connected with the detector elements in production. Moreover fewer electrical connection points results.
Furthermore, it has proven itself advantageous if, moreover, the function of the various components on the flexible printed circuit can already be tested before final mounting of the complete scanning unit and in this way defective units separated out.
Furthermore, in a preferred embodiment of the invention the scanning unit is not restricted to one definite scanning geometry but rather can be used in linear, rotary, incident-light, or transmitted-light measuring apparatuses, for example, as well as absolute and incremental position measuring apparatus.
Moreover it is ensured in this type of scanning unit, due to the small distance between the scanning graduation structure and the subsequently disposed optoelectronic components that a good optical separation with minimal cross-talk and low scattered light result.
In addition, the use of the flexible printed circuit, due to the relatively simple manageable prior out multi-layer technology, makes certain that any required conductor track crossovers can be realized simply, in particular, without expensive vacuum process technologies.
Furthermore, it follows as a further advantage that any mechanical stresses between the respective carrier bodies and the components disposed thereon due to the flexible printed circuit disposed therebetween can be minimized. Any possible thermal extension of the carrier body is transferred to the flexible printed circuit in this case, which compensates for this type of thermal effect.
Further advantages as well as the details of the inventive scanning unit follow from the following description of several exemplary embodiments with the aid of the accompanying figures.